European Journal of Organic Chemistry

Limonoid natural products are a large family of oxygenated terpenoid compounds that are best known as secondary metabolites found in citrus fruit. This Microreview provides a synopsis of the organic chemistry that has been applied over the last three decades to the synthesis of limonoid tetranortriterpenoids.

The organocatalytic β-alkynylation and β-alkenylation of aldehydes has just become much more practical: We present an improved procedure for the synthesis of β-carbonyl phenyltetrazolesulfones. X-ray crystallography, kinetic studies, as well as NMR and IR investigations of these compounds were performed.

A flexible and concise three-step protocol for the synthesis of functionalized dibenzothiophenes DBTs from readily available starting materials is presented. The method is based on two palladium-catalyzed reactions to prepare the masked thiophenols 4followed by deprotection and in situ cyclization to form the DBT skeleton. This approach offers improved functional-group tolerance as well as regiocontrol in the synthesis of functionalized DBTs as compared to previously reported methods.

An efficient and highly stereoselective total synthesis of an aliphatic depside (+)-bourgeanic acid via bourgeanic lactone and(–)-hemibourgeanic acid has been accomplished. A versatile desymmetrization strategy using Brown's asymmetric hydroboration was employed to install the complete stereochemistry of the natural product. This method provides the (+)-bourgeanic acid in 11 % overall yield.

Chiral dicationic Pd complex catalyzed enantioselective ene and aldol reactions with various isatin derivatives gave the corresponding 3-hydroxy-2-oxindole products bearing tertiary alcohols in high yields and enantioselectivities.

A highly enantioselective Friedel–Craftsalkylation of indoles with α,β-unsaturated aldehydes with excellent enantioselectivities (up to >99 % ee) has been developed, and this method offers substantial advantagesover traditional approaches, not only by avoiding the use of acids or bases, but also in terms of the high level of stereoselectivity.

Intramolecular excitation energy transfer in BODIPY-appended subporphyrins was found to occur from the subporphyrin to the BODIPY part. Fluorescence from BODIPY follows the intrinsic fluorescence properties of BODIPY references. meso-Oligo(1,4-phenylene) substituents can interact electronically with the subporphyrin core to cause redshifted absorption bands and to increased fluorescence quantumyields.

Enantiomerically pure ferrocene-based bis(phosphane) ligands combining three elements of chirality (C-central, P-central and planar) and bearing a trifluoromethyl group at a phosphorus atom were synthesized. Their complexes with transitionmetals were characterised and examined in an enantioselective Rh-catalyzed hydrogenation. The impact of the trifluoromethylated stereogenic phosphorus atom is described.

The first total synthesis of the marine alkaloid lamellarin S is described.

A tandem Ugi/Mitsunobu protocol, starting from o-aminophenols and α-hydroxy acids, gives benzo[b][1,4]oxazin-3-ones, with the introduction of up to four diversity inputs, in two high-yielding steps. The procedure may be carried out in a one-pot fashion and has a very broad scope, also allowing the synthesis of enantiomerically pure products.

Asymmetric Baeyer–Villiger oxidation of tricyclic cyclobutaone and a variety of racemic bicyclic cyclobutanone derivatives has been realized by the catalysis of 1,1′-bi-2-naphthol (BINOL)-derived chiral phosphoric acid with high yields and excellent enantioselectivities using 30 % aqueous H₂O₂ as the oxidant.

N@C₆₀-containing dimers have been proposed as quantum bits (qubits) for a quantum information processing device. Herein, we demonstrate the feasibility of synthesizing such dimeric systems, while at the same time retaining the extraordinary paramagnetic character of N@C₆₀.

A single thermodynamically favoured diastereomer has been formed by the reaction of (S)-2-(aminomethyl)pyrrolidine and tropos biphenol. This newly formed thiophosphoramide has proven to be an efficient bifunctional organocatalyst for the asymmetric Michael addition of cyclic ketones to nitro olefins, which afford the corresponding adducts with excellentdiastereo- and enantioselectivities.

The prolyl cis/trans amide rotamer populations of model peptides containing a proline mimetic constructed from a D-fructose scaffold have been explored. A conformational analysis was performed by molecular dynamics and NMR studies.

The asymmetric synthesis of 2-amino-5-oxo-5,6,7,8-tetrahydro-4H-chromene derivatives was achieved through a tandem Michael addition–cyclization reaction of easily available cyclohexane-1,3-dione and ethyl 2-cyano-3-phenylacrylates catalyzed by a chiral salen–cobalt(II) complex with moderate to good yields (up to 81 %) and high enantioselectivities (up to 89 % ee).

Clean tin's good! Efficiency of ionic liquid supported organotin reagents in Stille cross-coupling reactions involving aryl bromides has been investigated. Products were isolated with good yields by using a verysimple catalytic system. Organotin compounds were recycled without loss of activity and the contamination by tin was limited ([Sn] < 3 ppm).

Molecular tinkertoy: all-E-1,6-(Tributylstannyl)hexa-1,3,5-triene, all-E-1,8-(tributylstannyl)octa-1,3,5,7-tetraene, and related bis(tributylstannylated) polyenes undergomono-Sn/Li exchange reactions. They set the stage for terminus-differentiating functionalizations, which provide inter alianavenone B and (–)-cicutoxin.

The synthesis and binding properties of a calix[6]arene bearing a porphyrin at its large rim are described. It is shown that the host–guest adduct with a long-chain diamine displays strongly enhanced stability relative to the adducts formed with monoamines, which reveals the multipoint nature of the binding process.

New chiral non-racemic diselenides were prepared and their corresponding selenium electrophiles were used for the stereoselective functionalization of alkenes. The influence of different nucleophiles on the outcome of the selenenylation reaction was studied.

Application of the masked o-benzoquinone intramolecular Diels–Alder reaction in the total synthesis of platencin, a recently reported Fab-inhibitory antibiotic, has been demonstrated. The synthetic technology developed was further applied to the preparation of rationally designed analogues. Antibacterial studies of platencin and of synthesized analogues against a panel of normal and resistant strains are also reported.